Radiosignaling



March 4 1924.

H. G. CORDES RADIOS IGNALING Filed Sept. 29 1919 2 Sheets-Sheet l FIG.2.

INVENTOR W :9; emlw,

WWI/E8858:

2 Shets-Sheet 3 INVENTOR WIT "E8858:

Patented Mar. 4, 1924.

UNITED STATES HENRY ofconnrs, or nnnmnn'rorr, wasmne ron.

RADIOSIGNALING.

Application filed September 29, 1919. Serial R0. 827,818.

To aZZivhom it may concern:

Be it known that I, HENRY G. Comma, a

citizen of the United States, residing at Bremerton, in the] county ofKitsap and State of Washington, have invented a new and usefulImprovement in Radiosi aling.

My invention relates to a signal sifter 1n the receiving antenna circuitof a radio signal receiving system. 7

The object of my invention is to prevent or reduce the effect in areceiving system of undesirable signals of comparatlvely short durationand great intensity such as are produced by certain electricalatmospheric. disturbanoes or static while the effect of desirablesignals is only slightly reduced.

This object is attained by placing a signal sifter in series with thereceiving antenna circuit so that signals tending to produce currentexceeding a predetermined amplitude can not pass thru the sifter oraremade to pass thru the sifter with increased difiiculty' as the intensityof the undesirable signal increases. The presence of the sifter in. theantenna circuit introduces only a small additional resistance into thecircuit for currents of comparatively small amplitude which are producedby the desirable signals.

The sifter is particularly adapted for use in receiving sustained orconstant amplitude waves. The energy of a signal appears initially in areceiving antenna circuit as electrostatic energy. In case of desirablesustained wave signals a comparatively small amount of energy isreceived during each period of the natural period of the antennacircuit. In case of electrical impacts of com paratively short durationand great intensity which cause undesirable signals there is a largeamount of ener received by the antenna circuit which is issipated in atrain of oscillations having a high initial amplitude and persistingduring a correspondingly long period. These oscillations consist inelectrostatic energy being converted into electromagnetic energy and theelectromag netic energy converted again into electrostatic energy and soforth until all of the energy hasbeen dissipated. The advantage oflimiting the antenna circuit current 1s that only a limited part of theinitial electrostatic energy due to impact is converte intoelectromagnetic energy and therefore the train of oscillations islimited i intentact so that 800 micro-amperes flow 1n the sity andduration which is a great advantage in a receiving system.

The arrangement anduse of the sifter will be further explained byreference to the accompanying drawings forming part .of thisspecification. Figure 1 shows an elementary diagram of a receivingantenna circuit and signal sifter circuits. Figure 2 shows current-timecurves of currents in Figure 1. Figure '3 shows current-potentialrelations in Figure 1. Figure 4 shows a signal sifter using a thermioniccurrent vacuum tube. Figure 5 is a modification of Figure 1. Figure 6shows a. combined signal sifter and receiver. Figure 7 shows a modi fiedform of sifter vacuum tube.

In Figure 1 when the switch 2 is thrown to the left the receivingantenna circuit consisting of the antenna 1, antenna primary coil 3 andground connection 4 constitutes a receiving antenna circuit of thepresent radio art. The secondary coil 5 .is part of the usual receivingsystem. Coil 5 withdraws useful signal energy from the antenna circuit.To introduce the signal sifter into the antenna circuit throw switch 2to theright.

The signal sifter comprises a vacuum tube,

an arc circuit and an amplitude limitingl oil; 6 a

cuit. The vacuum tube ,6 has an ano three auxiliary anodes 8, 9 and 10and a mers5 cury cathode 11. The are circuit comprises a source 12 ofdirect current, a variab eresistance 13, choke coils 14' and 15', thearc anode 7 and the arc cathode 11. A resistance 16 is placed in shuntwith the source 12 so that a variable potential is available betweenpoints 17 and 18. The amplitude limiting circuit comprises a source ofvariable potential between points 17 and 18', a high resistance 19, adivided resistance 20, choke coils 21 and 22, anodes 8 and 9, cathode 11and choke coil 15. The third auxiliary anode 10 is a mercury anode usedfor starting an are from 7 to 11 and is similar to the usual startinganode of a mercury arc rectifier. f s

The operation of the sifter is as follows. Let 12'be a source'of 20 t'o30 volts direct current. Adjust resistance 13 so that a current of 5 to10 amperes flows in the arc circuit. Close switch 23 and tilt the vacuumtube in the usual manner to start an arc d from anode 7 to cathode-11.Open switch 23. Adjust the point 17 by a sliding conamplitude limitingcircuit. Divide resistance 20 so that the current from auxiliary anodes8 and 9 to cathode 11 is approximately equal. Choke coils 14 and 15prevent high frequency antenna current from flowing in the are circuitwhile choke coils 21 and 22 prevent high frequency current from flowingexternally between anodes 8 and 9.

It is well known mat when an arc is established between anode 7 andcathode 11 that current will flow, due to a comparatively low potential,from auxiliar" anodes 8 and 9 to cathode 11 but very littl e fromcathode 11 to anodes 8 and 9. The difierence of potential between theauxiliary anodes and the cathode remains ractically constant for varyingvalues oi current flowing from 8 or 9to 11. The direct current flowingfrom the auxiiiary or amplitude limiting circuit anodes 8 and 9 tocathode 11 is the amplitude limiting current. The current flowing from 8or 9 to 11 is the resultant of the amplitude limiting current and theantenna circuit current. This resultant current will'be designated, forconvenience, the Sifter current. When the maximum amplitude of theantenna circuit current equals 409 micro-amperes the sifter currentfluctuates between zero and 300 micro-amperes. Since current cannot flowfrom 11 to 8 or 9 the Sifter current cannot have a negative value. Ifthe direct current thru anode 8 is greater than the direct current thruanode 9 then the anode 9 sifter current will have a greater maximumvalue than the anode 8 sitter current. The resistance between aux iliaryanode 8 or 9 and cathode 11 varies practically inversely as the Siftercurrent. :The are vapor between Sifter anode 8 and cathode 11 and thearc vapor between sitter anode 9 and cathode 11 constitute twounidirectional current conductors in series with the antenna circuit.

In Figure 2 abscissas represent time and ordinates represent currentamplitude. Line 30 represents zero antenna current. Line 31 representszero anode 8 sifter current and line 32 represents zero anode 9 siftercurrent. With switch 2 thrown to the left, curve 33 represents desirablesignal antcnna current, curve 34 represents undesirable signal currentand curve 35 is the resultant of curves 33 and 34. Throw switch 2 to theright and the anode 8 sitter current is represented by line 36. Duringthe interval from 37 to 38 the curve 36 is a straight line whichindicates that the desirable signal current cannot pass thru the sitterduring this interval. If the undesirable signal is of short duration andcomparatively infra quent occurrence this blankin of the desirablesignal is not objectiona le. The antenna current due to the undesirablesi a1 is limited by line 36. The maximum initial current amplitude of atrain or free oscillations due to an undesirable signal is limited alsoby lines 31 and 32.

In Figure 3 the distance of any point from line 40, measured on alineparallel to line 41, represents potential and the distance of anypoint from line 41, measured on a line parallel to line 40, representscurrent. Curve or line 42 represents the average potential difi'erencebetween amplitude limiting anodes 8 and 9 during a half cycle, and curveor line 43 represents the average potential consumed by the primary coilv3 during a half cycle. Let the average potentiai consumed by the sifterbe e, and the average potential consumed by coil 3 be e For undesirablesignals of comparatively great intensity let the values of e, and e, beE and E respectively While the current is limited by the line 42.

The basis of my invention consists in the fact that the potential e, isless than c, for desirable signal current and E is greater than E forundesirable si nal current. In the first instance the use ul energywithdrawn from the antenna circuit is greater than the useful energydissipated in the Sifter. In the second instance the useless orundesirable energy dissipated in the sifter is greater than theundesirable energy consumed by coil 3. The Sifter also stops theconversion of much electrostatic undesirable energy into electromagneticenergy. For desirable signal potentials impressed upon the antennacircuit the line 42 should nearly coincide with line 40 but forundesirable signal potentials line 42 should be parallel to line 41. Thearrangement of Figure '1 gives the required constant potentialdifference for small variable current due to desirable signals anduni-directional conductivity to maintain constant current for variablehigh potentials due to undesirable signals. Any other arrangement whichgives a bend in curve 42 at the oint 44 or 45 may be used but apractically rlght angle bend is the ideal bend. The current-potentialcurves of crystal detectors and thermionic currents approachingsaturation give bends which may be utilized, provided that on part ofthe curve there 1s but a very slight potential variation for acomparatively large variation of current. The energy consumption of thesifter and coil 3 may be considered to vary practically as the averagepotentials altho the instants of maximum energy consumption of sitterand coil 3 for desirable signals are about 45 degrees out of phase. Thepotential E is limited to the average value indicated by theintersection of lines 42 and 43 in Figure 3. The presence of the sifterin the antenna circuit does not reduce the maximum instantaneouspotential impressed upon coil 3 by undesirable signals. Figure 4 shows asignal sitter arrangement using a thermionic current vacuum tube 50which has an incandescent filament 51, an anode 52, and a plate 53. Thistype of vacuum tube is described in the Proceedings of the Institute of'Radio Engineers of February, 1918, and is there designated as adynatron. Figure 4 is similar to Figure 1 when the switch 2 is thrown tothe left. The potential between the filament 51 and anode 52 and betweenfilament 51 and plate 53 is adjusted for zero current thruthenoninductive resistance 54. The voltage of battery 55 is 100 volts ormore. Inductance coil 56 allows direct current to pam to adjust thedirectcurrent thru 54 to zero or other suitable value to stabilize thedynatron while it does not allow high frequency antenna current, topass. A choke coil 57 'is placed in series with the anode to preventinduced high frequency current from flowing in this circuit. The largecondenser 58 shunts part of the battery 55 for hlgh frequency antennacurrent.

The Sifter is introduced into the antenna circuit by throwing switch 2to the right. A low potential impressed upon the antenna circuit bydesirable signals is nearly all consumed by coil 3 but a high potentlal1mpressed upon the circuit is mostly consumed by the sitter and themaximum amphtudeof the undesirable signal current is limited for acomparatively large range of high 1mpressed potential. A small antennacurrent thru non-inductive resistance 54 causes a large potentialdifierence between the terminals of 54 which may be utilized instead ofcoil 3 for withdrawing energy from the antenna circuit.

Figure 5 is similar to Figure. 1 except that -the amplitude limitingcircuit has only oneanode and consists of a source of variable potentialbetween points 17 and 18, high resistance 19, choke coil 21, anode 8,cathode 11 and choke coil 15. The amplitude relations of vFigure 2 applyto Figure '5 except that either line 31 or 32 is omitted, that is, thecurrent amplitude is limited only in one direction. Current in theantenna circuit is not limited in the direction from anode 8 to cathode11 but it is limited in the direction from cathode 11 to anode 8. Thisarrangement prevents free oscillations having a high initial amplitudeand the energy loss in the sifter due to desirable signal currentis onlyone half of the loss of Figure 1. The disadvantage of this arrangementis that a secondary circuit coupled to the antenna circuit may receivean impact due to an undesirable si al and oscillate with a high initialamp itude at its own natural frequency which is as undesirable in asecondary circuit as in the antenna circuit. This arrangement istherefore suitable only for an antenna circuit having no secondaryoscillatory circuit.

Figure 6 shows an arrangement in which a single vacuum tube is used forboth detector and sitter. The sifter arrangement is similar to Figure 1.The are circuit consists of battery 12, choke coil 14, anode 7, cathode11, choke coil 15 and resistance 13. The amplitude limiting circuitcomprises the source of variable potential between points 17 and 18, theresistance 19, the divided resistance 20, hoke coils 21 and 22, anodes 8and 9, cathode 11, choke coil 15 and resistance 13. The function of theabove arrangement is the same as in Figure 1.

The receivin s in detail by Pierce in Pat'ent No. 1,112,549, datedOctober 6, 1914. A battery 60 and telephone receiver 61 are connected inseries between anode 7 and plate 62. A condenser 63 is connected inparallel with coil 5 to form the usual secondary oscillatory circuit ofa receiving system. The condenser 63 and coil 5 are connected in serieswith a small condenser 64 between the anode 7 and grid 65. Theoscillatory current in 5 and 63 due to desirable signal current variesthe conductivity ofthe rarefied gas path from plate 62'to anode 7 byvarying the potential between anode 7 and 'd 65. As the potential variesbetween 7 an 65 the direct current varies thru the telephonev receiver61 and produces audible sound. The are anode 7 is provided with a hole66 thru which the space above 7 becomes properly ionized. A platinumpoint 67 holds the cathode spot" in the center of the mercury pool. Theadvantage of this arrangement is that the same vacuum arc is used forboth the detector'and the sitter. The sifter may be cut out of theantenna circuit by closing the switch 68.

Figure 7 shows a vacuum tube having a tungsten cathode 11 in rarefiedargon. The filament 70 is heated by closing switch 71 to facilitatestarting an are between the anode 7 and cathode 11. The amplitudelimiting circuit anodes 8 and 9 are placed close to the arc and have asemi-cylindrical form. The energy required to maintain a proper arc inthis tube is less than in the tube of Figure 1. r

The function of the sitter can be made still moreclear by comparing itwith a sieve. Small particles pass thru the mesh of a sieve withoutexertin much pressure on themesh but large partic es do not pass thruand exert a pressure on the mesh. This is analogous to small amplitudecurrent passing thru the signal sifter without much potential differencebetween the terminals of the Sifter while large amplitude current cannotpass thru the signal sifter and the potential difference between theterminals is comparatively large as shown by Figure 3. The largeparticles also prevent small particles from passing thru the mesh of asieve. Simtem shown is described 1 ilarly, a high potential impressedupon the antenna circuit tending to produce large amplitude currentprevents small amplitude current from passing thru the sifter, as shownby Figure 2. The duration of the impressed high potential may becompared to the speed with which large particles pass over the mesh.Many large particles passing over a single mesh sieve at slow speedcompared to the speed of small particles would seriously interrupt thesifting of small particles. Similarly, many electrical impacts ofcomparatively long duration will interrupt reception of the desirablesignal. If an arrangement were used which would give that part of line42, Figure 3, which is parallel to line 41 a positive and decreasingslope as the amplitude of the current increased then undesirable signalcurrent would pass thru the sifter with increased difiiculty as theamplitude of the current increased. This may be compared to a flexiblemesh thru which particles would pass with increasing difficulty as thesize of the particles increased. The strength of the amplitude limitingcurrent corresponds to the size of a mesh of a sieve.

The sifter can be used in a receiving cir-- cuit which is in proximityto a sending station only when means are provided to reduce theamplitude of the interfering signal current in the receiving antennacircuit, as is done in duplex signalling. If the interfering signal is aconstant frequency sinoidal wave having a low rate of change ofamplitude then a, parallel resonance circuit tuned to the interferingwave and placed in series with the receiving antenna circuit willcounteract the interfering signal.

The construction of the sifter vacuum tube or valve presents no specialfeatures not found in the construction of vacuum tube rectifiersgenerally. The amplitude limiting circuit anodes should be placed closeto the cathode spot so that the space between anodes and cathode isthoroly ionized but the anodes must be kept cool enough to prevent anobjectionable amount of inverse current.

A galvanometer may be placed in series with the amplitude limitingcircuit to measure the maximum current which can flow in the antennacircuit.

The capacitance between the terminals of the sifter due to capacitanceof leads, distributed capacitance of coils and capacitance betweenterminals inside the tube should be reduced to a minimum especially whenthe capacitance of the antenna circuitjs small.

Energy to actuate a radio signal detector is generally withdrawn fromthe antenna circuit by means of a, coupled reactance. Energy isdissipated by the sifter in the form of heat. All energy in a receivingantenna circuit is either withdrawn to actuate a detector. dissipated asheat or re-radiated when prevented from being transformed intoelectromagnetic energy in the antenna circuit.

The terms oscillating current and oscillatory circuit as used in thisspecification refer respectively to the current in'a circuit or to acircuit which comprises inductance and capacitance and has less than thecritical resistance required to make the current in the circuitnon-oscillatory. The general term rarefied gas conductor refers toeither a vacuum arc vapor conductor or to a thermionic currentconductor, that is, the conductivity in rarefied gas may be due eitherto ionization by collision or to pure electron conduction which isgenerally considered to be independent of the presence of gas, or it maybe due to both gasand electron conduction as in Fig. 7.

The novel features of my invention are more definitely stated in thefollowing claims.

I claim:

1. The combination of an alternating current circuit, means forimpressing both high and low electromotive forces upon said circuit,means for limiting the current in said circuit when said highelectromotive force is impressed upon said circuit and means forreducing to a nearly zero value the resistance of said second-mentionedmeans to the flow of alternating current in said circuit when said lowelectromotive force only is impressed upon said circuit, saidsecond-mentioned means being connected serially in saidl circuit.

2. In an alternating current amplitude limiter, a conductor havingunidirectional conductivity, means for producing a flow of directcurrent thru said conductor and means for superposing alternatingcurrent of limited amplitude upon said direct current thru saidconductor; said conductor having the property of a constantinstantaneous potential drop for variable current of limited amplitudethru said conductors 3. An alternating current circuit in combinationwith means for limiting positive and negative amplitudes of alternatingcurrent in said circuit and means for keeping anearly constantinstantaneous potential drop thru said first-mentioned means only whensaid current has an amplitude of limited value, said first-mentionedmeans being serially connected in said circuit.

4. An alternating current amplitude limiter comprising a rarefied gascontainer having a cathode, a plurality of anodes and auxiliary meansfor producing arc vapor in said container in combination with means forproducing a flow of direct current from said anodes to said cathode.

5. The combination of an oscillatory circuit comprising inductance andcapacitance Masses and means for limiting the amplitude of oscillatingcurrent in said circuit; said means having the property of introducingless than the critical non-oscillatory resistance into said circuit.

6. In means for limiting the amplitude of current in an oscillatingcurrent circuit the combination of two conductors in series in saidcircuit, the potential drop for limited current thru one of saidconductors being positive, the potential drop for limited current thruthe other of said conductors being negative and the total drop forlimited current thru said conductors in series being nearly zero; saidconductors comprisin a rarefied gas conductor.

An alternating current circuit wherein are combined an anode, an arcvapor conductor, a cathode, a second arc vapor conductor and a secondanode in series connected serially with said circuit, auxihary means forproducing said vapor and a source of direct current connected to saidanodes and to said cathode.

8. Means for translating radiant energy into oscillating current energy,said means comprising a radiant-energy-absorbing oscillatory circuit andmeans for limiting the rate at which said radiant energy can betranslated into electromagnetic energy in said circuit.

9. The method of reducing the duration of a train of free oscillationsin an oscillatory circuit of a radio receiving system which consists inlimiting the amount of electrostatic energy in an oscillato circuitwhich can be transformed into e ectromagnetic energy.

10. The met 0d of varying the current limit in an oscillatory circuitcomprising a current amplitude limiter which consists in superposing anoscillating current upon a direct current and varying the value of saiddirect current.

11. The method of limiting the amplitude of oscillating current by meansof a conductor having unidirectional conductivity and. whose resistancevaries [pram tically 'inversel as the current thru said conductor whicconsists in superposing an oscillating current whose amplitude is to belimited upon a direct current thru. said conductor.

12. The method of minimizing the eifective resistance introduced into analternat ing current circuit by placing a current amplitude limiter inseries therewith, said limiter comprising a conductor havingunidirectional conductivity which consists in passing said currenthaving an amplitude less than a fixed value thru said limiter at nearlyzero instantaneous potential dro during a complete cycle of said currentan passing said current tending to have an amplitude greater than saidfixed value at a substantial potential drop.

13. The method of limiting the current thru the capacitance of anoscillatory circuit having a conductor comprising rarefied gas in serieswith said circuit which consists in discharging a limited charge on saidcapacitance thru said conductor at. nearly zero potential drop anddischarging a charge on said capacitance which is materially greaterthan said limited charge thru said conductor at a potential drop of asubstantial value. f

14. The method. of overcoming undesirable effects in an oscillatorycircuit comprising inductance and capacitance which consists in limitingthe amplitude of oscillating current thru said inductance andcapacitance when comparatively large electromotive forces are impressedon said circuit and in securing the cumulative efiects of comparativelysmall electromotive forces impressed on said circuit.

15. An alternating current circuit in combination with means forlimiting both positive and negative current amplitudes in said circuit,said means comprising a conductor having the properties ofunidlrectional conductivity and constant potential drop for a variablecurrent of limited amplitude.

16. The combination of an antenna circuit, means for translating energyfrom said circuit to a secondar circuit and means for limiting the rate0; translating said energy to said secondary circuit; saidlast-mentioned means comprising a unidirectional current conductor inseries with the antenna circuit and having the. property of apractically constant potential drop when variable current of limitedamplitude flows thru said conductor.

This specification -led and witnessed.

this 22nd day of Septem 1 r, 1919. c

* 1 Y G. CORDES.

